The present invention relates to a bearing assembly and particularly to a self-lubricating bearing assembly which provides greater operational life than is presently available.
More particularly, the present invention relates to a bearing assembly comprising co-engaging inner race and outer race members movable relative to one another wherein the inner race has a bearing surface provided with a self-lubricating bearing material which is engageable with and movable relative to the bearing surface of the outer race. The races are made from a metal and titanium is preferred.
Conventional track roller bearings are constructed of rolling elements positioned between inner and outer races, lubricated by grease. Periodic lubrication is required to maintain operational performance with added resistance to corrosion. Such bearings are subject to failure where fracturing of the rolling elements and spalling of the inner race occur. The performance of these known track roller bearings also depends on the effectiveness of the seals associated therewith which not only insures that the grease lubrication is maintained within the bearing proper but also that contamination from external sources is avoided.
A bearing assembly which is an alternate to the above-described rolling element--track roller assembly is known, this alternate incorporating a self-lubricating liner system affixed to the inner surface of an outer race which operates against the bearing surface of a hardened inner race. These bearing assemblies do not require periodic lubrication and they generally have higher rolling load capacity than the aforementioned rolling element-track roller bearings. Also, the static radial load capacity of these alternate bearing assemblies is substantially higher than the rolling element type bearings with high thrust capacity being ensured by the use of the separate self-lubricating liner system. Such an alternate self-lubricating type bearing assembly is disclosed for instance in U.S. Pat. Nos. 4,048,370 and 4,134,842.
It has been found, however, that the lubricating material fixed to the outer race in track-roller bearing assemblies is subject to distortion and consequent reduced service life relative to the claimed arrangement due to induced liner deflection when loaded by the inner race during rotation of the outer race. This condition adversely affects the bond between the lubricating material and the outer race, and as the bond fails, the lubricating material is pinched between the inner and outer races without any support and tends to be squeezed out.
Known track-rollers are constructed utilizing a self-lubricating liner system attached to the inside diameter of the outer race with the belief that the wear experienced during the life of the bearing system would be distributed over the full circumference of the liner system and thus result in extended service life expectancy. However, it has been observed that due to the rotation of the outer race self-lubricating liner in relation to the stationary inner race and the unidirectional load application, liner systems with compression modulus up to about 1,000,000 psi are subjected to material deflection. The mismatch of the inner race circumferential surface to the outer race by differential tolerances and the thickness of the liner system provide the mechanism which permits local deflection of the liner system as the outer race translates to the stationary inner race when loaded. Therefore, liner systems when reacted with a steady applied load, while moving in relation to the inner race, impose high shearing action and tensile forces on the liner immediately in front of the progressing load action of the inner race, which is known as ploughing. When combined with fluid contamination, the liner system is further distressed due to the wedging action of the fluid in front of the advancing inner race slider.
It has now been found that the bearing assembly of the present invention avoids this liner bond failure occasioned by the above described ploughing action and exhibits a significantly extended wear life. In the bearing assembly of the present invention the self-lubricating bearing material is provided on the outer bearing surface of the inner race member rather than, as in prior art bearings, on the inner bearing surface of the outer race. This construction ensures positive contact between liner system and mating surface, so that fluid contamination does not become a mechanical wedging tool as it does in known self-lubricating track rollers. The present invention precludes the deflection of the liner system which creates a shear lip thereby causing high shearing forces within the liner. The liner system adhered to the outside diameter of the inner race does not permit hydraulic wedging due to fluid contamination. The limited wear surface of this configuration allows a number of additional wear surfaces which can be positioned by reindexinq the inner race in relation to the primary load application. Thus, the bearing assembly of the present invention comprises an inner race member the outer surface of which constitutes a bearing surface provided with a self-lubricating bearing material, and an outer race member having an inner bearing surface coengaging and movable relative to the self-lubricating bearing material fixedly secured to the outer bearing surface of said inner race.
The drawings show a preferred embodiment of the invention but it will be understood that various changes may be made from the construction disclosed and that the drawings and description are not to be construed as defining or limiting the scope of the invention.